1. Field of the Invention
The present invention relates to an image heating apparatus used for an image forming apparatus, such as copiers and laser beam printers, employing an image-forming process, such as electrophotography and electrostatic recording.
2. Description of the Related Art
Some image heating apparatuses used for an image forming apparatus may have a cylindrical belt, a nip portion forming member in contact with an inner surface of the belt, and a pressure member for forming a nip portion through the belt together with the nip portion forming member. The image heating apparatus described above may generally heat a toner image while conveying a recording material which bears the toner image by the nip portion. The image heating apparatus described above may be adapted to have the belt formed thin so that heat capacity can be small, thereby allowing for the merit of a shorter period needed to warm up the image heating apparatus.
And now, recently, there has been required a technology for further shortening the warm-up period. Japanese Patent Application Laid-Open No. 2007-57827 discloses an apparatus configured in a manner that, at warm-up operation, a fixing belt having an electrically conductive layer is spaced apart from a pressure member, and the fixing belt is brought into contact with the pressure member after the fixing belt reaches a fixable temperature.
However, in the case of the image heating apparatus disclosed in Japanese Patent Application Laid-Open No. 2007-57827, the fixing belt is locally heated due to electromagnetic induction, and accordingly the fixing belt has to be configured so that it can be driven to rotate for warming the entire circumference of the fixing belt at warm-up even if the fixing belt is spaced apart from the pressure member. If the fixing belt, as shown in Japanese Patent Application Laid-Open No. 2007-57827, is driven using an end cap attached to an end of the fixing belt, and a drive gear, then the fixing belt needs to have rigidity to some extent. However, an increase in thickness and rigidity of the fixing belt leads to a larger heat capacity of the fixing belt, resulting in a longer warm-up time. Accordingly, even if the fixing belt is spaced apart from the pressure member at warm-up in a configuration in which the fixing belt is locally heated, a shortening effect of the warm-up time may be unfortunately reduced.